Захотел молочка от бычка

This man will not help you or give it to you because he cannot; where nothing is nothing can be obtained. See Как с быком ни биться, а молока от него не добиться (K)

Cf: It is very hard to shave an egg (Br.). Look not for musk in a dog's kennel (Br.). No man can flay a stone (Am., Br.). Tis very hard to shave an egg (Am,). You cannot get blood from a turnip (Am,). You cannot get blood out of a stone (Am., Br.). You can't draw water from a dry well (squeeze water from a stone) (Am.). You seek cold water under cold ice (Am.)